The grooving of thin-walled metal pipe is well-known in the art, and, has particular advantage in those circumstances in which the roll-grooved thin-walled pipe is to be employed in conjunction with a segmented pipe coupling.
The roll-grooving of such thin-walled metal pipe can readily be accomplished by a groove rolling machine, a typical example of such a roll grooving machine being that shown in Thau, Jr. et al U.S. Pat. No. 3,903,722 issued Sep. 9th, 1975.
Segmented pipe couplings also are well known in the art, typical examples being those shown in Blakely U.S. Pat. No. 3,695,638 issued Oct. 3rd, 1972, in Webb U.S. Pat. No. 4,601,495 issued Jul. 22nd, 1986, and, Rung et al, U.S. Pat. No. 4,639,020 issued Jan. 27th, 1987. The segmented pipe couplings disclosed in those patents have equal applicability to pipe or fittings that have been machine cut grooved, in which event the pipe must be of appreciable thickness in order to accommodate the cutting of the groove, and, to thin-walled pipe in which a groove has been provided by a rolling operation performed on the thin-walled metal pipe.
Typically, in the groove rolling of long lengths of thin walled metal pipe, the pipe is supported on a cradle, which permits rotation of the pipe about the longitudinal axis of the pipe as the roll-grooving operation proceeds. There also exists the possibility of skewing the cradle, and thus the longitudinal axis of the pipe, relative to the longitudinal axes of the respective grooving rollers. Skewing of the axis of the thin-walled metal pipe relative to the axes of the grooving rollers is essential in order to inhibit spiraling of the pipe off the female grooving roller, and out of the pinch of the respective male and female grooving rollers, which otherwise will occur due to distortion produced in the pipe end during the rolling operation, as is well known in the art.
While this is less of a problem in the event that a long length of thin-walled metal pipe is to be grooved at its end, it does pose problems in circumstances where a short length of thin walled metal pipe is to be grooved. To effect roll grooving of short length of thin-walled metal pipe, either a special jig has to be provided to hold the short length of pipe with its longitudinal axis appropriately skewed relative to the axes of rotation of the grooving rollers, or, it is necessary for the short length of thin-walled metal pipe to be manually held, positioned and manipulated during the groove rolling operation, particularly at the commencement of the groove rolling operation.
Thin-walled metal pipe typically is pipe formed from an iron or steel, or formed from copper or stainless steel, stainless steel thin-walled metal pipe exhibiting the smallest wall thickness of the pipe, and, in turn, exhibiting the greatest tendency to spiral off the female grooving roll during the rolling operation, the extremely thin walled stainless steel metal pipe being more readily deformable during the rolling operation than its more substantial iron, steel counterparts.
The reasons why thin-walled metal pipe must be restrained against spiraling off the female grooving roll and why the axis of the thin-walled metal pipe must be skewed relative to the axes of the grooving rollers is discussed later in this specification.